Vehicle will not move in drive or reverse and Check Engine light is on

What is your question?

Yesterday I got my Trailblazer back from AAMCO after having the transmission replaced because AAMCO told me that the flywheel went out and damaged other parts of the transmission. Last night when the transmission went into reverse it sounded like I had backed into something at about 40 mph. This morning the vehicle would not move in drive or reverse and the Check Engine Light is on. What could be causing this problem?